The present invention relates to water hammer arresters. Water hammer arresters are devices for preventing the development of water hammer in conduits conveying water under pressure and under conditions of interrupted flow.
The phenomenon of water hammer is caused by the development of hydraulic shock waves generated by the sudden stopping of fluid flow within the confines of a conduit system carrying water under pressure. This condition results from the rapid closing of positive valves incorporated within the system. In addition to the production of unpleasant noise effects, fluid hammer, if allowed to persist for any length of time, will result in broken conduits and damage to other components of the conduit system.
Various types of water hammer arresters are known in the prior art. Some devices include expandable bellows or diaphragms that absorb the shock. Another type of water hammer arrester involves the application of a piston working against the pressure developed by a compressed gas chamber. When the water hammer arrester is properly installed with its inlet orifice facing the pressurized water supply line, it must reduce spike pressures as high as 1,000 p.s.i. or more (in large pipe diameters) to 150 p.s.i. or less. Nevertheless, an echo effect still results from the dampening effect of the initial spike shock.
Conventional piston-type water hammer arresters are typically manufactured from copper tubing with solder attached brass/copper fittings that provide either pipe thread or sweat solder fittings in order to install into the supply lines. They utilize either brass or plastic pistons with a number (2-3) of rubber o-ring seals. Some problems exist with this particular design. In order to reduce the echo effect it is necessary to utilize acoustical/fluid directional methods to break up shock wave patterns. For example, there have been some experiments with conical interiors of the body and limiting orifices to improve and reduce echo.
Long term life conditions of this design of water hammer arrester are also a concern. Hard deposits of iron, calcium, and or sand, which exist in all municipal water, infiltrate the rubber o-rings due to a clearance gap much larger than these contaminant particle sizes. When this infiltration occurs, the hard deposits are imbedded into the o-rings, especially due to a silicone grease requirement used to lubricate the o-rings. This imbedding of deposits causes scoring of the interior wall of the copper tubing and degradation of the o-rings. In time, the pressurized chamber (normally 60 p.s.i.) behind the piston leaks and is absorbed into the water supply. The resulting loss of pressure renders the water hammer arrester ineffective.
Another problem with conventional water hammer arresters is denting of the thin-walled copper body. During installation, when a plumbing contractor may have personnel installing hundreds of water hammer arresters, fatigue occurs and heavy wrenches required for the installation work are dropped and may strike the thin-walled copper body causing a dent that may prevent piston movement.
There have been water hammer arresters formed entirely out of plastic. However, the pipe thread connections may easily cross thread or fracture during installation.
What is needed is a water hammer arrester that will reduce echo, provide superior dent resistance, improve long term life and provide a high strength non-corrosive metallic connection to the supply lines.
The present invention meets the above-described need by providing a water hammer arrestor having an insert molded plastic body with a metal attachment at one end to install to the supply line. A piston disposed inside the bore of the plastic body includes a flexible skirt that faces the water supply. The skirt includes a sharp edge that provides a scraping/cleaning action.